/*
silverPDF is sponsored by Aleyant Systems (http://www.aleyant.com)

silverPDF is based on PdfSharp (http://www.pdfsharp.net) and iTextSharp (http://itextsharp.sourceforge.net)

Developers: Ai_boy (aka Oleksii Okhrymenko)

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above information and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR SPONSORS
BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.

*/
#region PDFsharp - A .NET library for processing PDF
//
// Authors:
//   Stefan Lange (mailto:Stefan.Lange@pdfsharp.com)
//
// Copyright (c) 2005-2008 empira Software GmbH, Cologne (Germany)
//
// http://www.pdfsharp.com
// http://sourceforge.net/projects/pdfsharp
//
// Permission is hereby granted, free of charge, to any person obtaining a
// copy of this software and associated documentation files (the "Software"),
// to deal in the Software without restriction, including without limitation
// the rights to use, copy, modify, merge, publish, distribute, sublicense,
// and/or sell copies of the Software, and to permit persons to whom the
// Software is furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included
// in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
// THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
// FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER 
// DEALINGS IN THE SOFTWARE.
#endregion

using System;
using System.Diagnostics;
using System.Text;
using PdfSharp.Internal;
using PdfSharp.Pdf.Internal;

namespace PdfSharp.Pdf.Filters
{
  /// <summary>
  /// Implements the ASCII85Decode filter.
  /// </summary>
  public class ASCII85Decode : Filter
  {
    /// <summary>
    /// Encodes the specified data.
    /// </summary>
    public override byte[] Encode(byte[] data)
    {
      if (data == null)
        throw new ArgumentNullException("data");

      int length = data.Length;  // length == 0 is must not be treated as a special case
      int words = length / 4;
      int rest = length - (words * 4);
      byte[] result = new byte[words * 5 + (rest == 0 ? 0 : rest + 1) + 2];

      int idxIn = 0, idxOut = 0;
      int wCount = 0;
      while (wCount < words)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16) + ((uint)data[idxIn++] << 8) + data[idxIn++];
        if (val == 0)
        {
          result[idxOut++] = (byte)'z';
        }
        else
        {
          byte c5 = (byte)(val % 85 + '!');
          val /= 85;
          byte c4 = (byte)(val % 85 + '!');
          val /= 85;
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');

          result[idxOut++] = c1;
          result[idxOut++] = c2;
          result[idxOut++] = c3;
          result[idxOut++] = c4;
          result[idxOut++] = c5;
        }
        wCount++;
      }
      if (rest == 1)
      {
        uint val = (uint)data[idxIn++] << 24;
        val /= 85 * 85 * 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
      }
      else if (rest == 2)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16);
        val /= 85 * 85;
        byte c3 = (byte)(val % 85 + '!');
        val /= 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
        result[idxOut++] = c3;
      }
      else if (rest == 3)
      {
        uint val = ((uint)data[idxIn++] << 24) + ((uint)data[idxIn++] << 16) + ((uint)data[idxIn++] << 8);
        val /= 85;
        byte c4 = (byte)(val % 85 + '!');
        val /= 85;
        byte c3 = (byte)(val % 85 + '!');
        val /= 85;
        byte c2 = (byte)(val % 85 + '!');
        val /= 85;
        byte c1 = (byte)(val + '!');

        result[idxOut++] = c1;
        result[idxOut++] = c2;
        result[idxOut++] = c3;
        result[idxOut++] = c4;
      }
      result[idxOut++] = (byte)'~';
      result[idxOut++] = (byte)'>';

      if (idxOut < result.Length)
        Array.Resize<byte>(ref result, idxOut);

      return result;
    }

    /// <summary>
    /// Decodes the specified data.
    /// </summary>
    public override byte[] Decode(byte[] data, FilterParms parms)
    {
      if (data == null)
        throw new ArgumentNullException("data");

      int idx;
      int length = data.Length;
      int zCount = 0;
      int idxOut = 0;
      for (idx = 0; idx < length; idx++)
      {
        char ch = (char)data[idx];
        if (ch >= '!' && ch <= 'u')
          data[idxOut++] = (byte)ch;
        else if (ch == 'z')
        {
          data[idxOut++] = (byte)ch;
          zCount++;
        }
        else if (ch == '~')
        {
          if ((char)data[idx + 1] != '>')
            throw new ArgumentException("Illegal character.", "data");
          break;
        }
        else
        {
          // ingnore unknown character
        }
      }
      // Loop not ended with break?
      if (idx == length)
        throw new ArgumentException("Illegal character.", "date");

      length = idxOut;
      int nonZero = length - zCount;
      int byteCount = 4 * (zCount + (nonZero / 5)); // full 4 byte blocks

      int remainder = nonZero % 5;
      if (remainder == 1)
        throw new InvalidOperationException("Illegal character.");

      if (remainder != 0)
        byteCount += remainder - 1;

      byte[] output = new byte[byteCount];

      idxOut = 0;
      idx = 0;
      while (idx + 4 < length)
      {
        char ch = (char)data[idx];
        if (ch == 'z')
        {
          idx++;
          idxOut += 4;
        }
        else
        {
          uint val =
            (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
            (uint)(data[idx++] - '!') * (85 * 85 * 85) +
            (uint)(data[idx++] - '!') * (85 * 85) +
            (uint)(data[idx++] - '!') * 85 +
            (uint)(data[idx++] - '!');

          output[idxOut++] = (byte)(val >> 24);
          output[idxOut++] = (byte)(val >> 16);
          output[idxOut++] = (byte)(val >> 8);
          output[idxOut++] = (byte)val;
        }
      }

      // I've found no appropriate algorithm, so I write my own. In some rare cases the value must not
      // increased by one, but I cannot found a general formula or a proof.
      // All possible cases are tested programmatically.
      if (remainder == 2) // one byte
      {
        int idxIn = idx;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85);

        // Always increase if not zero (tried out)
        if (value != 0)
          value += 0x01000000;

        output[idxOut++] = (byte)(value >> 24);
      }
      else if (remainder == 3) // two bytes
      {
        int idxIn = idx;
        uint val;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85);

        if (value != 0)
        {
          value &= 0xFFFF0000;
          val = value / (85 * 85);
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');
          if (c1 != data[idxIn] || c2 != data[idxIn + 1] || c3 != data[idxIn + 2])
          {
            value += 0x00010000;
            //Count2++;
          }
        }
        output[idxOut++] = (byte)(value >> 24);
        output[idxOut++] = (byte)(value >> 16);
      }
      else if (remainder == 4) // three bytes
      {
        int idxIn = idx;
        uint val;
        uint value =
          (uint)(data[idx++] - '!') * (85 * 85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85 * 85) +
          (uint)(data[idx++] - '!') * (85 * 85) +
          (uint)(data[idx++] - '!') * 85;

        if (value != 0)
        {
          value &= 0xFFFFFF00;
          val = value / 85;
          byte c4 = (byte)(val % 85 + '!');
          val /= 85;
          byte c3 = (byte)(val % 85 + '!');
          val /= 85;
          byte c2 = (byte)(val % 85 + '!');
          val /= 85;
          byte c1 = (byte)(val + '!');
          if (c1 != data[idxIn] || c2 != data[idxIn + 1] || c3 != data[idxIn + 2] || c4 != data[idxIn + 3])
          {
            value += 0x00000100;
            //Count3++;
          }
        }
        output[idxOut++] = (byte)(value >> 24);
        output[idxOut++] = (byte)(value >> 16);
        output[idxOut++] = (byte)(value >> 8);
      }
      return output;
    }

    //public static int Count1;
    //public static int Count2;
    //public static int Count3;
  }
}
